The present invention relates to a system for injecting a fuel, especially gasoline, into an internal combustion engine and more particularly a fuel injection system for an internal combustion engine, which controls the quantity of the fuel to be injected into the engine so that the quantity of the fuel may vary in linear relation with the variation of the quantity of an intake air induced into the engine.
There have been deviced and demonstrated many types of fuel injection systems for internal combustion engines. One type is provided with fuel metering device for metering the continuously flowing fuel, depending upon the quantity of air inducted into the engine, and the metered fuel is continuously injected through fuel injection nozzles attached to the intake pipe or duct of the engine. In the fuel metering device, a variable orifice is located in a fuel passage and operatively coupled to a sensor for detecting the intake air flow rate or the quantity of the intake air inducted into the engine. In addition, the fuel metering device includes a differential pressure regulating valve so that the differential pressure across the variable orifice may be maintained at a predetermined level. Therefore, the variable orifice controls the flow rate of the fuel which continuously flows through the fuel passage.
In another type, the fuel is metered by a Jerk type fuel injection pump provided with a solid cam control device which is actuated in response to the rotational speed of the engine and depending upon the degree of opening of a throttle valve, whereby the air-fuel ratio is controlled. The metered fuel is intermittently injected through a fuel injection nozzle into each cylinder of the engine.
In the former type described above, the intake air passage has a very complex configuration so that the quantity of intake air may be in proportion to the angular displacement of the shaft of the sensor which in turn causes the displacement of a piston or plunger type valve member of the fuel control device. Furthermore, in order to reciprocate the plunger to which the pressure of the fuel is exerted, the sensor must generate the pressure higher than the pressure of the fuel acting upon the plunger. Therefore, the sensor is, in general, large in size and complicated in construction.
More particularly, the plunger of the fuel metering device is operatively coupled to a supporting arm connected to a sensor valve or vane in such a way that the supporting arm acts as a lever on the plunger increasing the force acting on the lower end of the plunger to overcome the pressure of the fuel acting upon the upper end of the plunger. Therefore, in order to increase the driving force applied to the plunger, the size of the sensor valve or vane must be increased so that the area upon which the air pressure acts may be increased. Further, the lever or supporting arm must be increased in size so that the increased force may be applied to the plunger. Therefore, the intake air sensor becomes large in size and complicated in construction. The intake air sensor of the type described presents another problem that the distance between the intake air sensor and the fuel metering device is limited because the plunger of the latter is coupled to the supporting arm of the former through the mechanical linkage so that the intake air sensor and the fuel metering device cannot be mounted in their respective suitable positions.
In the fuel injection system of the type using a Jerk type fuel pump, there is an advantage in that the fuel may be injected under a high pressure so that the satisfactory atomization of the fuel may be attained. However, the quantity of the fuel to be injected is controlled in response to the rotational speed of the engine and to the degree of opening of a throttle valve. That is, the quantity of the fuel is not controlled directly depending upon the quantity of the intake air inducted into the engine. As the result, the quantity of the fuel to be injected is not corrected or compensated even when the quantity of the intake air varies due to the wear of the engine and the variation in accuracy accompanied with the assemble parts. Consequently, the air-fuel ratio cannot be controlled with a desired degree of accuracy. In addition, in case of a multi-cylinder engine, the Jerk type pumps equal in number to the cylinders must be provided so that the fuel injection system is very complex in construction. Furthermore, this system includes a large number of parts which must be machined and finished with a higher degree of accuracy so that the manufacturing cost is high. Moreover the Jerk type fuel injection pumps are large in size and heavy in weight so that it is extremely difficult to mount them on a vehicle.
In view of the above, according to the present invention a fuel injection system comprises the fuel pressure control device for detecting the intake air flow rate or the quantity of the intake air inducted into the engine and for controlling the fuel pressure in response to the intake air flow rate and fuel metering device which meters the fuel in response to the operation of the fuel pressure control device, said fuel metering device having a control shaft which is operatively and hydraulically coupled to the fuel pressure control device. To the end of the present invention therefore, there is provided a fuel injection system which very simple in construction and compact in side and which can intermittently deliver the fuel accurately in proportion to the quantity of the intake air to be inducted into the engine.
Another object of the present invention is to provide a fuel pressure control device which is very simple in construction and compact in size.
A further object of the present invention is to provide a fuel metering device which may be easily mounted on the engine.
Accordingly to one preferred embodiment of the present invention, the fuel pressure control device includes a control orifice which is defined by a circumferentially partially extended parallel slit formed on the inner surface of a cylindrical bearing and a cutout portion of a sensor valve shift fitted into the bearing so that the opening of the control orifice may be varied depending upon the quantity of intake air, thereby controlling the quantity of the fuel to be injected. A fuel differential pressure regulating valve is provided in order to maintain the differential pressure across the control orifice at a predetermined level, and the parallel slit is formed in parallel with the surface of the cutout portion of the sensor valve shaft. Therefore, the quantity of the fuel flowing through the control orifice varies in linear relation with the quantity of the intake air.
Since there is a fixed orifice for limiting the flow rate of the fuel at the upstream of the control orifice, the fuel changes in pressure in proportion to the square of the opening area of the control orifice. The opening area of the control orifice changes as a function of sin.sup.2 (.theta./2), where .theta. is the angle of rotation of the sensor valve shaft. Therefore, the pressure of the fuel varies as a function of sin.sup.2 (.theta./2).
The area of the opening defined between the sensor valve and the air duct in the fuel pressure control device changes as a function of the angle of rotation .theta. of the sensor valve shaft. When the air duct is rectangular in cross section, the opening area varies approximately as a function of sin.sup.2 (.theta./2). When the cross section of the air duct is so compensated that the opening area may be varied precisely as a function of sin.sup.2 (.theta./2), and since there may be provided an intake air differential pressure regulating valve which may maintain the differential pressure across the sensor valve at a predetermined level, the intake air flow rate or the quantity of intake air varies as a function of sin.sup.2 (.theta./2).
From the above relation, it is naturally resulted that the fuel pressure varies with the intake air flow rate or the quantity of intake air in the ratio of 1:1.
When the pressure of the fuel is applied to the control shaft of the fuel metering device, the displacement of the control shaft changes with the pressure of the fuel at the constant ratio of 1:1. Since the pressure of the fuel changes as a function of sin.sup.2 (.theta./2) while the quantity of intake air changes also as a function of sin.sup.2 (.theta./2), the displacement of the control shaft changes in linear proportion to the quantity of intake air.
For the sensor valve which may satisfy the above relations, it is only necessary to operate to overcome against its return spring. Thus a sensor valve or vane small in size may be used in practice. As a result, the fuel pressure control device can be made compact in size.
The displacement of the control shaft of the fuel metering device is effected by the pressure of the fuel so that the fuel metering device may be hydraulically communicated with the fuel pressure control device through a pipe line or the like. Therefore, the fuel metering device is possible to be mounted in any suitable position so that its mountability is improved.
Since the supplying pressure of the fuel to the internal combustion engine is used as the operating pressure for the control shaft of the fuel metering device, no special hydraulic circuit is required for delivering the hydraulic pressure to drive the control shaft.
The above and other objects, features and advantages of the present invention will become more apparent from the following description of the preferred embodiments thereof taken in conjunction with the accompanied drawings.